Skip coverage upload for merge queue runs

Merge queue commits are ephemeral — coverage was already uploaded
during the PR, and the push to the default branch will upload
results for the final landed commit. Log a warning and exit
successfully instead of wasting an API call.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

action.yml

@@ -34,6 +34,14 @@ runs:
           exit 1
         fi
 
+        # Skip coverage upload for merge queue runs — coverage should be
+        # uploaded for PRs and the default branch, making merge queue
+        # uploads unnecessary.
+        if [ "${{ github.event_name }}" = "merge_group" ]; then
+          echo "::warning::Skipping coverage upload for merge queue. Configure your workflow to upload coverage for PRs and the default branch instead. To avoid spinning up a runner, add \"if: github.event_name != 'merge_group'\" to the upload job."
+          exit 0
+        fi
+
         # Skip coverage upload for fork PRs — the token won't have write
         # permissions to the base repository.
         if [ "${{ github.event.pull_request.head.repo.full_name }}" != "" ] && \